According to the American Heart Association nearly 383,000 out-of-hospital sudden cardiac arrests occur annually in the United States. These subjects may be saved by the timely application of life saving measures such as Cardiopulmonary resuscitation (CPR).
CPR is a well-known and valuable method of first aid used to resuscitate people who have suffered from cardiac arrest. CPR requires repetitive chest compressions to squeeze the heart and the thoracic cavity to pump blood through the body. Artificial respiration, such as mouth-to-mouth breathing or a bag mask apparatus, is used to supply air to the lungs. When a first aid provider performs manual chest compression effectively, blood flow in the body is about 25% to 30% of normal blood flow. However, even experienced paramedics cannot maintain adequate chest compressions for more than a few minutes. Hightower, et al., Decay In Quality Of Chest Compressions Over Time, 26 Ann. Emerg. Med. 300 (September 1995). Thus, CPR is not often successful at sustaining or reviving the subject. Nevertheless, if chest compressions could be adequately maintained, then cardiac arrest victims could be sustained for extended periods of time. Occasional reports of extended chest compression efforts (45 to 90 minutes) have been reported, with the victims eventually being saved by coronary bypass surgery. See Tovar, et al., Successful Myocardial Revascularization and Neurologic Recovery, 22 Texas Heart J. 271 (1995).
In efforts to provide better blood flow and increase the effectiveness of bystander resuscitation efforts, various mechanical devices have been proposed for performing automated chest compressions. There are currently two types of automated chest compression devices. One type uses a belt placed around the subject's chest to effect chest compressions. The AutoPulse® chest compression is one such device, and is described in patents such as Mollenauer, et al., Resuscitation Device having a Motor Driven Belt to Constrict/Compress the Chest, U.S. Pat. No. 6,142,962 (Nov. 7, 2000). The other type uses a piston which repeatedly compresses the chest. Piston based chest compression systems include the LUCAS® chest compression device (illustrated in Sebelius, et al., Rigid Support Structure on Two Legs for CPR, U.S. Pat. No. 7,569,021 (Aug. 4, 2009)) and the THUMPER® chest compression device (illustrated in Barkolow, Cardiopulmonary Resuscitator Massager Pad, U.S. Pat. No. 4,570,615 (Feb. 18, 1986). These chest compression systems include a piston and a motor for repeatedly driving the piston downwardly on the chest, and lifting the piston from the chest to allow the chest to expand under its own natural resistance.
As mechanical compressions are performed by piston based chest compression systems, the compression components may shift position relative to the subject. When an automated chest compression system does not apply chest compressions to the appropriate location on the subject's chest the effectiveness of the automated chest compressions are diminished. The repeated extension and retraction of the piston often results in the piston moving or “walking” up the subject's chest toward the neck or moving down toward the subject's abdomen.